Right from the early 1970, the Unix OS had, as usual, an elegant and powerful system in place for managing the security of shared objects on the system. These objects included files and directories—perhaps the most commonly thought of ones. Files, directories, and symbolic links are filesystem objects; there are several others, including memory objects (tasks, pipes, shared memory regions, message queues, semaphores, keys, sockets) and pseudo filesystems (proc, sysfs, debugfs, cgroupfs, and so on) and their objects. The point is all these objects are shared in some manner or other, and thus they require a protection mechanism of some sort, to protect them from abuse; this mechanism is called the Unix permission model.
You probably don't want others to read, write, and delete your files; the Unix permission model makes this possible...